Synthetic Gear Oil Info Request

After searching and reading the info on the site about synthetic trans/gear oil it seems like it has possibilities for use in my trans and rear end. Because of the cost of swithing over I'd like the member opionions. My trans is a 5 speed manual. My driving is aproximarely 95% rural county roads up to 45 mph and 5% highway driving. It will cost me about $125 to swith over both the trans and rear end. What type of benefits can I expect? Does the cost justify the benefits?

For product service life in differentials, consult your owner’s manual or the Original Equipment Manufacturer (OEM) to establish the application, NORMAL or SEVERE..

Normal Service​

Severe Service​

Cars, SUVs, Light TrucksDrain at 100,000 miles of service or according to the owner’s manual, whichever is longerDrain at 50,000 miles of service or according to the owner’s manual, whichever is longerHeavy Duty Class 8 Line HaulFollow the OEM drain interval (miles or hours) for synthetic oil up to 250,000 miles or three years, whichever comes first. Otherwise, drain at twice the OEM interval for conventional oil.Vocational/DeliveryFollow the OEM drain interval (miles or hours) for synthetic oil up to 120,000 miles or three years, whichever comes first. Otherwise, drain at twice the OEM interval for conventional oil.Heavy Duty Off-RoadFollow the OEM drain interval (miles or hours) for synthetic oil up to 100,000 miles or two years, whichever comes first. Otherwise, drain at twice the OEM interval for conventional oil.

After searching and reading the info on the site about synthetic trans/gear oil it seems like it has possibilities for use in my trans and rear end. Because of the cost of swithing over I'd like the member opionions. My trans is a 5 speed manual. My driving is aproximarely 95% rural county roads up to 45 mph and 5% highway driving. It will cost me about $125 to swith over both the trans and rear end. What type of benefits can I expect? Does the cost justify the benefits?

I was going to have it done at the local GM Dealership for the sake of convenience. And I think it would be easier than rolling around in my drive way. My truck is an 07 GMC Sierra Classic 5 speed m/t. The synthetic oil is 75-90 GL4 according to the dealer.